Gliding:
(1) Every landing a forced landing.
(2) Spend an entire weekend hanging around the airfield for ten minutes in the air.
(3) Even more sensitive to weather (ie even more weather cancellations) than powered flight.
Powered:
(1) Costs more. Just a bit.
(2) Noisier, if you like the idea of silent flight.
But, with powered flight you just turn up, fly your hour and go home, and you can (sometimes) fly in weather that keeps gliders on the ground.
You pays your money and you takes your choice. No reason not to do both, if you've got lots of time and lots of money.